The problem of underwater noise is a hydra: manifold, complex, and mutable. It cannot be addressed simply, locally, or with data culled from just one species or region. A recent U.S. Ocean Studies Board panel found anthropogenic noise is doubling per decade, whereas another recent Marine Mammal Commission panel was unable to reach consensus on research and mitigation priorities because of insufficient data. We lack data on noise trends in any marine habitat, and we have audiometric data on fewer than 100 marine species, with even less data on noise-induced threshold shifts. Despite considerable recent research, we are far from understanding the mechanisms and scope of underwater noise impacts. Essentially, we do not know what, where, or how sound is having an impact on any marine organism.